PRIOR CONCURRENT THERAPY: Biologic therapy: No prior anticancer biologic therapy Chemotherapy: See Disease Characteristics No prior oxaliplatin No prior adjuvant irinotecan Prior adjuvant fluorouracil and leucovorin calcium allowed At least 3 weeks since prior chemotherapy (e.g., second-line irinotecan with or without fluorouracil (or capecitabine) and leucovorin calcium) for metastatic disease and recovered Endocrine therapy: Not specified Radiotherapy: At least 3 weeks since prior radiotherapy No prior radiotherapy to target lesion unless documented progression within the radiation portal Surgery: See Disease Characteristics At least 4 weeks since prior surgery for primary tumor or metastases and recovered Other: No prior investigational anticancer drug No other concurrent investigational agents